1. Field of the Invention
This invention relates to a transfer apparatus which transmits drive power from an engine of a vehicle to a front wheel, a rear wheel, or both a front wheel and a rear wheel of the vehicle. More particularly, the invention relates to a transfer apparatus equipped with a differential mechanism in which an input shaft and a plurality of pinion shafts are connected to each other.
2. Description of Related Art
In four-wheel-drive vehicles, transfer apparatuses equipped with center differential lock mechanisms have previously been used for transmitting drive power from engines to front and rear wheels. Transfer apparatuses which employ differential mechanisms having bevel gearing in order to reduce their sizes in radial directions are described, for example, in U.S. Pat. No. 3,923,113 and Japanese Unexamined Patent Publication No. 1-164,629. By using a differential mechanism having bevel gearing, the size of the mechanism, in a radial direction thereof, can be reduced as compared to a center differential mechanism having planetary gearing. Moreover, when a speed differential arises between the front and rear wheels, the speed differential is absorbed by the center differential mechanism, so that the occurrence of slip is effectively prevented.
However, by using a differential mechanism having bevel gearing, even though the size of the mechanism in its radial direction is reduced, its size in the axial direction is large or long. This is because in the center differential mechanism, a sprocket for transmitting drive power to the front wheels of the vehicle, a center differential lock mechanism and a differential limit mechanism are disposed, in this order, in the axial direction. As a result, it is difficult to obtain an overall compact transfer apparatus structure.
In another previously known transfer apparatus, a clutch mechanism, forming at least part of a differential limit mechanism for limiting a speed differential between the front and rear wheels, is provided at the periphery of a bevel gear. This is because the clutch mechanism is provided between differential side gears which mesh with differential pinion gearing provided at a pinion shaft. Consequently, because the clutch mechanism is provided, the size of the transfer apparatus, in a radial direction, becomes larger than is acceptable. As a result, it is difficult to obtain a compact apparatus.
Additionally, since the clutch mechanism is inevitably provided at the periphery of the bevel gear, it is also difficult to support an input shaft within a transfer casing. This can cause the input shaft to be unstably supported.